The parameters determined in blood gas analysis, pH, Po.sub.2, and Pco.sub.2, are sensitive to influence from the outside environment, and thus it is necessary to take special precautions in order to avoid such influences. This need is well known in the art and patent literature relating to sampling devices for the above-mentioned purpose is comprehensive.
Different classes of sampling devices for use in connection with blood gas analysis are well known. One class of devices comprises syringes with a piston part, which under the influence of the arterial blood pressure are pushed backwards during the filling of the syringe from a starting position with the piston part fully advanced. Another class of devices comprises flattened flexible containers from which air has been expelled prior to sampling. However, a certain amount of air will remain in devices of these two classes, and precautions intended to get rid of even these traces have been disclosed.
Another type of blood sampling device for arterial blood sampling basically comprises a gas-filled sampler reservoir provided with an inlet opening as well as a venting passage to the ambient atmosphere, the venting passage having valve means cooperating therewith. Vented sampling devices of this class are well-known, e.g., from the following patent publications: published Danish patent application No. 5494/72 and corresponding U.S. Pat. Nos. 3,943,917, 4,340,067, DK Nos. 2736/78, 2737/78, EP Nos. 0047806, 0047176, U.S. Pat. No. 4,299,238, DE Nos. 3018262, 3041563, U.S. Pat. Nos. 4,266,559, 4,266,558, 4,257,426, 4,206,768, 4,172,448, 4,133,304, 3,978,846, 3,960,139, 3,785,367 and WP No. 8103426.
Use of some of the well-known vented blood sampling devices requires manipulations of certain kinds in order to achieve a liquid-tight sealing of the sample reservoir. Also known are vented blood sampling devices of this type which automatically, i.e., without manipulation, permit passage of gas but not the liquid blood sample for providing a liquid-tight sealing of the venting passage. One of these devices is disclosed in the above-mentioned U.S. Pat. No. 4,340,067 and has incorporated a piece of paper material between the piston part and the walls of the sample reservoir, the paper material forming a venting means or a passageway through which air is exhausted as blood enters the chamber under arterial pressure. The passageway is automatically closed to prevent leakage from the chamber when the chamber becomes filled with blood and the paper material is wetted.